Plastic deformation of magnesium single crystal: a crystal plasticity coupled twinning phase field simulation

A crystal plasticity coupled twinning phase field (CP-TPF) model was developed to investigate the plastic deformation of magnesium (Mg) single crystal. Three types of slip systems, i.e., basal, prismatic, and pyramidal slip ones were considered in the crystal plasticity model, while the crystalline, gradient, and elastic energies were considered in the phase field model for twinning. The results show that during the twinning induced by the shear loading along the twinning direction, the stress levels at different stages and the mobility of twin interfaces in different directions show huge differences. The twins are lenticular at the early stage and show a flat plane during the growth, and the activation of basal slip follows the twinning deformation. Non-basal slip is activated after the matrix is completely transformed into the twins. Different plastic deformation modes are observed in Mg single crystal with different crystalline orientations during one tensile-compressive loading cycle: The corresponding deformation modes are twinning-detwinning-pyramidal slip-retwinning when the loading direction is parallel to the c axis and are prismatic slip-twinning prismatic slip-twinning-detwinning when the loading direction is perpendicular to the c axis of the single crystal, a strong tension-compression asymmetry is shown in both the two simulations; while only the basal slip occurs, and no tension-compression asymmetry is observed when the angle between the loading direction and the c axis is 45°.